1. Field of the Invention
The present invention relates to a gas burner including a plurality of flame openings aligned in a parallel arrangement for discharging a mixture of a fuel gas and combustion air.
2. Description of the Prior Art
According to a known gas burner, as shown in FIG. 37, a mixer 403 is connected to a burner body 402 with a plurality of flame openings formed by means of a multi-pore plate member 401. In operation, the mixer 403 mixes a fuel gas from a pipe passage 404 with a combustion air from a blower 8 to feed in distribution a same mixture gas, which has a stable self-combustible air-fuel ratio (air excess ratio:=1.2 to 1.5), to all the flame openings to be burned on the surface of multi-pore plate member 401. Such construction is known from e.g. U.S. Pat. No. 4,480,988.
However, with the above-described gas burner, there tends to occur lift phenomenon in the flame in association with increased load in the combustion chamber. Further, there often occurs incomplete combustion in association with a change in the air excess ratio. Thus, the burner still has room for improvement in terms of extension in the turn-down ratio and of combustion stability. Also, it has been very difficult for the above gas burner to satisfactorily achieve all of the desired performances of low NOx and noise generations and a high load combustion.
More specifically, if the air excess ratio is increased within the stable self-combustible range in order to sufficiently reduce the NOx generation, this will disturb the stability of flame formation to generate a greater combustion noise and also to disadvantageously reduce the heat generation and consequently the combustion load. Reversely, if the air excess ratio is decreased in order to increase the combustion load, this will increase the temperature of flames thereby to increase the NOx generation. Moreover, since such high temperature region will be formed most conspicuously in the immediate vicinity of the surface of the multi-pore plate member 401, the resonance inside the burner body 402 will increase, whereby the burner will generate a greater noise in this case also.
Further, when the burner is first ignited, since the surface of the multi-pore plate member 401 is at a low temperature, there occurs insufficient surface combustion, which tends to lead to incomplete combustion.